From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Mon, 23 Dec 2002 10:15:27 -0600 From: Dave McCracken Subject: Re: shared pagetable benchmarking Message-ID: <45600000.1040660127@baldur.austin.ibm.com> In-Reply-To: <3E037690.45419D64@digeo.com> References: <3E02FACD.5B300794@digeo.com> <9490000.1040401847@baldur.austin.ibm.com> <3E037690.45419D64@digeo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: linux-mm@kvack.org List-ID: --On Friday, December 20, 2002 11:59:12 -0800 Andrew Morton wrote: > So changing userspace to place its writeable memory on a new 4M boundary > would be a big win? > > It's years since I played with elf, but I think this is feasible. Change > the linker and just wait for it to propagate. Actually it'd require changes to both the linker and the kernel memory range allocator. Right now ld.so maps all memory needed for an entire shared library, then uses mprotect and MAP_FIXED to modify parts of it to be writable (or at least that's what I see using strace). If it was done using separate mmap calls we could redirect the writable regions to be in a different pmd. >> Let's also not lose sight of what I consider the primary goal of shared >> page tables, which is to greatly reduce the page table memory overhead of >> massively shared large regions. > > Well yes. But this is optimising the (extremely) uncommon case while > penalising the (very) common one. I guess I don't see wasting extra pte pages on duplicated mappings of shared memory as extremely uncommon. Granted, it's not that significant for small applications, but it can make a machine unusable with some large applications. I think being able to run applications that couldn't run before to be worth some consideration. I also have a couple of ideas for ways to eliminate the penalty for small tasks. Would you grant that it's a worthwhile effort if the penalty for small applications was zero? Dave McCracken ====================================================================== Dave McCracken IBM Linux Base Kernel Team 1-512-838-3059 dmccr@us.ibm.com T/L 678-3059 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/